The present invention relates to microfluidic devices, and more particularly, to the moving and detecting fluids with respect to a microfluidic device.
Methods of making a homologous series of compounds, or the testing of new potential drug compounds comprising a series of light compounds, has been a slow process because each member of a series or each potential drug must be made individually and tested individually. For example, a plurality of potential drug compounds that differ perhaps only by a single amino acid or nucleotide base, or a different sequence of amino acids or nucleotides are tested by an agent to determine their potential for being suitable drug candidates.
The processes described above have been improved by microfluidic chips which are able to separate materials in a micro channel and move the materials through the micro channel is possible. Moving the materials through micro channels is possible by use of various electro-kinetic processes such as electrophoresis or electro-osmosis. Fluids may be propelled through various small channels by the electro-osmotic forces. An electro-osmotic force is built up in the channel via surface charge buildup by means of an external voltage that can repel fluid and cause flow.
In fluid delivery in microfluidic structures, several layers comprise the device. Channels often extend between the various layers. A capillary break structure is used in place of a valve downstream of an electrohydrodynamic pump in a channel. The capillary break is a location where the small channel ends abruptly as the entrance to a larger space. Capillary forces pull the fluid up to the end of the small cross-section channel but not beyond. This stops the fluid flow until additional pressure is provided. Prior to pushing fluid beyond the capillary break, a gap or discontinuity occurs in the fluid path immediately downstream of the capillary break. This prevents cross-contamination from other fluid paths.
In some instances, an electrohydrodynamic pump generates a relatively low pressure and may not be able to overcome the capillary break without an additional pressure applied. Also, size, uniformity, and other fabrication tolerances cause variances in the effectiveness of electrohydrodynamic pumps. Also, the mircofluidic chip is preferably designed to be used with several different types of fluid. The variation of fluid properties, such as composition and temperature, also affect the ability of an electrohydrodynamic pump to overcome the capillary break.
Another difficulty in using capillary breaks is knowing whether or not the capillary break has actually been overcome. It is currently assumed that if a sufficient amount of pressure is provided that the capillary break is overcome. But as mentioned above, fabrication tolerances and functional characteristics may vary due to each capillary break. Thus, some capillary breaks may actually not be overcome. Likewise, it would be desirable to know whether or not a capillary break has been cleared.
It would, therefore, be desirable to enable a capillary break to be overcome for various fabrication tolerances and fluids used within the microfluidic device. It would also be desirable to sense the proper operation of a capillary break.
It is, therefore, one object of the invention to provide an improved fluid delivery mechanism to an array of reaction wells.
It is a further object of the invention to reliably overcome a capillary break in spite of manufacturing tolerances.
In one aspect of the invention, a microfluidic device has a layer with a capillary break formed by a capillary sluice. The capillary sluice has a lower surface and an upper surface. A first electrode is disposed on the lower surface. The first electrode is coupled to the voltage source. A second electrode spaced a predetermined distance from the first electrode coupled to the voltage source.
One advantage of the invention is that feedback from the electrodes may be used by the controller and the software therein to adjust the operation of the microfluidic device.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.